N. S. Saxena

Activation energy and crystallization kinetics of untreated and treated oil palm fibre reinforced phenol formaldehyde composites

Abstract In this paper, oil palm fiber reinforced phenol formaldehyde (PF) treated, as well as untreated, composites have been taken for the study. The untreated sample (sample 1) contains oil palm fiber reinforced in the PF matrix, and the same fiber is treated with silane (sample 2) and with alkali (sample 3) to produce two types of treated fibers. These treated fibers were then reinforced in the matrix to produce two treated samples. Differential scanning calorimetry has been employed to study the crystallization kinetics and the energy of crystallization for all the samples. All the samples show the well-defined peaks of crystallization. In the case of silane-treated sample, double crystallization is observed. The crystallization data are analyzed in terms of a modified Kissinger’s equation to determine the activation energy. The activation energy and other crystallization parameters have also been determined using Matusita’s equation and are compared with the values obtained from other equations. It has also been found that various treatments have improved the thermal stability of the composites to different extents.

Thermal properties of pineapple leaf fiber reinforced composites

Simultaneous measurment of effective thermal conductivity (λ) and effective thermal diffusivity (κ) of pineapple leaf fiber reinforced phenolformaldehyde (PF) composites have been studied by transient plane source (TPS) technique. The samples of different weight percentage typically (15, 20, 30, 40 and 50%) have been taken. It is found that of effective thermal conductivity and effective thermal diffusivity of the composites decrease, as compared with pure PF as the fraction of fiber loading increases. Using Y. Agari, model thermal conductivity of pure fiber is evaluated and compared with the thermal conductivity of fiber determined by extrapolated experimental value of composite. Also, we have compared the results of thermal conductivity of composites with two models (Rayleigh–Maxwell and Meredith–Tobias model). Good agreement between theoretical and experimental result has been found.

Glass Transition Phenomena, Crystallization Kinetics and Enthalpy Released in Binary Se100–xInx (x = 2, 4 and 10) Semiconducting Glasses

Results of Differential Scanning Calorimetry (DSC) under non-isothermal conditions on Se 100-x In x (x = 2, 4 and 10) glasses are reported and discussed. The glass transition region has been investigated in terms of activation energy and the dependence of glass transition temperature Tg on coordination number with varying composition and heating rates. The crystallization kinetics and its dimensionality have been studied using two different models viz. Matusita and Ozawa equations. On the basis of the obtained experimental data the temperature difference T c - Tg and the enthalpy released, ΔH c , are found to be maximum and minimum, respectively, for Se 96 In 4 glass which indicate that this glass is the thermally most stable in the composition range of investigation.

Enthalpy recovery during structural relaxation of Se96In4 chalcogenide glass

Abstract Structural relaxation of isothermally and isochronally heat-treated Se 96 In 4 chalcogenide glass in the glass transition region has been studied using a differential scanning calorimeter (DSC). The recovery of excess enthalpy Δ H excess has been calculated from the knowledge of excess apparent specific heat Δ C p ,a ( T ) and plotted as a function of annealing time t a . Δ H excess has been found to vary with t a ; this variation follows a power-law behaviour and an expression of the form Δ H excess =Δ H o [ t a ] y has been proposed to describe such variation . Following the Kissinger formalism the activation energy of structural relaxation E t , both for annealed and un-annealed samples, has been obtained. The so obtained values of structural relaxation activation energies are indicative of the fact that some kind of bond interchange has taken place which in turn accounts for the relaxation process in Se 96 In 4 glass. From the knowledge of Δ H excess ( T a , t a ) and the corresponding activation energy, the activation energy spectra have also been drawn and discussed.

Structural, optical and electrical properties of CdZnS thin films

The thin films of Cd1-x Zn x S (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) have been prepared by the vacuum evaporation method using a mechanically alloyed mixture of CdS and ZnS. The structural, optical and electrical properties have been investigated through the X-ray diffractometer, spectrophotometer and Keithley electrometer. The X-ray diffraction patterns of these films show that films are polycrystalline in nature having preferential orientation along the (002) plane. In the absorption spectra of these films, absorption edge shifts towards lower wavelength with the increase of Zn concentration. The energy band gap has been determined using these spectra. It is found that the energy band gap increases with increasing Zn concentration. The electrical conductivity of so prepared thin films has been determined using a I–V characteristic curve for these films. The result indicates that the electrical conductivity decreases with increasing Zn content and increases with temperature. An effort has also been made to obtain activation energy of these films which increases with increasing Zn concentration in CdS.

Glass transition phenomena, crystallization kinetics and thermodynamic properties of ternary Se80Te20−xInx (x=2, 4, 6, 8 and 10) semiconducting glasses: theoretical and experimental aspects

Abstract This paper presents the results of kinematical studies of glass transition and crystallization in glassy Se 80 Te 20− x In x ( x =2,4, 6, 8 and 10) using differential scanning calorimetry (DSC). Also the thermodynamic properties of these glasses in the transformation range of temperatures have been studied. Glass transition region has been investigated in terms of activation energy, dependence of glass transition temperature on coordination number with the varying composition and heating rates. The growth kinetics and its dimensionality have been investigated using three different models viz. Kissinger, Ozawa and Matusita equations. On the basis of the obtained experimental results on phase transformations in these glasses, thermodynamic parameters like entropy difference between metastable states in the glassy region, difference of Gibbs free energy, specific heat, entropy between the two phases and the enthalpy released during crystallization have been determined. On the basis of experimental observations and theoretical calculations of thermodynamic properties, it has been found that Se 80 Te 10 In 10 is the most stable glass.

Kinetic Studies of Bulk Se85—xTe15Sbx Glasses with x = 0, 2, 4, 6, 8 and 10

Results of Differential Scanning Calorimetry (DSC) under non-isothermal condition of Se 85-x Te 15 Sb x (x = 0, 2, 4, 6, 8 and 10) glasses are reported and discussed. The glass transition temperature at different heating rates and structural changes during glass transition have been determined from an empirical relation. The activation energies for crystallization have been determined from the heating rate dependence of the peak crystallization temperatures. The results have been analyzed using Kissingers and Matusitas equations and the modified Ozawa equation for non-isothermal crystallization of materials. The variation of the glass transition temperature with composition suggests that a small amount of Sb(4 at%) leads to an increase in the chain length of Se-Te, whereas further increase in the Sb atomic percentage increases the number of Se-Te chains in the alloys. The thermal stability (T c - T g ) is found to be maximum at 4 at% Sb and suggests that this alloy can be considered as a critical composition at which the system becomes chemically ordered. Moreover, the minimum heat released during crystallization at this composition confirms the maximum stability of the alloy.

Kinetic studies of bulk Ge22Se78-xBix (x=0, 4 and 8) semiconducting glasses

Results of phase transformations, enthalpy released and specific heat of Ge22Se78−xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, Tg, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of Tg (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of Tg, at a heating rate of 5 K min−1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol−1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference Tc−Tg and the enthalpy released during the crystallization process. Below Tg, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.

Simultaneous measurement of thermal conductivity and thermal diffusivity of some building materials using the transient hot strip method

A transient hot strip method developed by Gustafsson (1979), for simultaneous measurement of thermal conductivity and thermal diffusivity of solids and fluids with low electrical conductivity, is used for the simultaneous measurements of thermal conductivity and thermal diffusivity of some building materials such as dry dune sand, dry brick powder, dry cement, dry mud powder and dry asbestos powder at room temperature and normal pressure. The hot strip works both as a plane heat source and a temperature sensing device. The experimental values of thermal conductivity and thermal diffusivity of these materials are compared with those obtained from thermal probe and hot-wire methods. A good agreement in the values indicates that the transient hot strip (ThS) method can also be used for loose porous materials for obtaining these thermal parameters.

Differential scanning calorimetry studies of Se85Te15−x Pb x (x = 4, 6, 8 and 10) glasses

Results of differential scanning calorimetry (DSC) studies of Se85Te15−xPbx (x = 4, 6, 8 and 10) glasses have been reported and discussed in this paper. The results have been analyzed on the basis of structural relaxation equation, Matusita’s equation and modified Kissinger’s equation. The activation energies of structural relaxation lie in between 226 and 593 kJ/mol. The crystallization growth is found to be onedimensional for all compositions. The activation energies of crystallization are found to be 100–136 kJ/mol by Matusita’s equation while 102–139 kJ/mol by modified Kissinger’s equation. The Hruby number (indicator of ease of glass forming and higher stability) is the highest for Se85Te9Pb6 glass while S factor (indicator of resistance to devitrification) is highest for Se85Te7Pb8 glass at all heating rates in our experiment. Further the highest resistance to devitrification has the highest value of structural activation energy and the activation energy of crystallization is maximum for the most stable glass by both Matusita’s equation and the modified Kissinger’s equation.